Typical personal headlamps are shown in U.S. Design patents D405202 dated Feb. 2, 1999, and D470615, dated Feb. 18, 2003. In most cases, the headlamp is supported on the wearer's head by a headstrap, in the form of a band of flexible material, usually a stretchable fabric, adapted to fit about an individual's head so that the headlamp is supported on the forehead. The headstrap extends through slots in a bracket attached to an assembly comprising one or more incandescent bulbs or light-emitting diodes, a reflector, a switch, and associated electrical wiring or control circuitry. The assembly may include a power source compartment for containing one or more electrochemical cells (“batteries”). However, in the case of higher power headlamps, the power source compartment is often a separate unit at a location remote from the light-emitting device or devices.
One of the problems encountered by users of personal headlamps is that drainage of the power source can result in inopportune loss of illumination. Moreover, it is usually difficult to replace the batteries, especially in the dark, and when the power source compartment is closed by screw fasteners or the like, so that a tool is required to open it. Failure of the headlamp can also occur due to filament burn-out in the case of an incandescent bulb, and for various other reasons such as mechanical failure of a switch, or corrosion due to moisture. There is a need, therefore, for a suitable auxiliary illumination device to serve as a back-up source of illumination in the event of failure of the primary headlamp.
Carrying a second headlamp or flashlight as a spare is generally not a practical solution, especially in hiking and other activities where pack weight minimization is important. Moreover, providing two headlamps on a single headstrap is unwieldy, and requires the user to carry significant additional weight.